Recent technological advances have led to complementary metal-oxide-semiconductor (CMOS) sensor imagers being leveraged by cameras, video systems, and the like. CMOS sensor imagers can include an integrated circuit with an array of pixel sensors, each of which can comprise a photodetector. Moreover, a CMOS sensor imager can be incorporated into a System-on-Chip (SoC). As such, the SoC can integrate various components (e.g., analog, digital, . . . ) associated with imaging into a common integrated circuit. For instance, the SoC can include a microprocessor, microcontroller, or digital signal processor (DSP) core, memory, analog interfaces (e.g., analog to digital converters, digital to analog converters), and so forth.
Visible imaging systems implemented using CMOS imaging sensors can reduce costs, power consumption, and noise while improving resolution. For instance, cameras can use CMOS imaging System-on-Chip (iSoC) sensors that efficiently marry low-noise image detection and signal processing with multiple supporting blocks that can provide timing control, clock drivers, reference voltages, analog to digital conversion, digital to analog conversion and key signal processing elements. High-performance video cameras can thereby be assembled using a single CMOS integrated circuit supported by few components including a lens and a battery, for instance. Accordingly, by leveraging iSoC sensors, camera size can be decreased and battery life can be increased. Also, dual-use cameras have emerged that can employ iSoC sensors to alternately produce high-resolution still images or high definition (HD) video.
A CMOS imaging sensor can include an array of pixel cells, where each pixel cell in the array can include a photodetector (e.g., photogate, photoconductor, photodiode, . . . ) that overlays a substrate for yielding a photo-generated charge. A readout circuit can be provided for each pixel cell and can include at least a source follower transistor. The pixel cell can also include a floating diffusion region connected to a gate of the source follower transistor. Accordingly, charge generated by the photodetector can be sent to the floating diffusion region. Further, the imaging sensor can include a transistor for resetting the floating diffusion region to a predetermined voltage level prior to charge transference.
In a CMOS imaging sensor, pixel cells in the pixel array are light collecting devices controlled by circuits of digitally controlled transistors. Various light integration modes can be employed by the CMOS imaging sensor. For instance, in full frame integration mode, each pixel cell can be integrated or exposed to a light source at times during the duration of a full frame time except when the pixel is being read and reset. This mode can allow for the maximum amount of light to be integrated in each pixel cell, which can provide high signal integration. Further, in sub-frame integration mode, each pixel cell can be integrated or exposed to a light source for a period of time that is less than a full frame time while maintaining the same frame rate as for the full frame integration mode.
Pixel cells are reset in the course of operation, which is oftentimes effectuated by opening a circuit to a voltage source via digital control to yield a current draw. When employing full frame integration mode, one row of pixel cells can be reset during a particular time period. However, when sub-frame integration mode is effectuated, multiple rows of pixel cells can be reset during a common time period. Typical approaches leveraged for resetting pixel cells oftentimes employ a common current source. Thus, concurrent resetting of more than one pixel cell from differing rows in the pixel array can be infeasible with conventional techniques when sub-frame integration mode is utilized since a current supplied to each of these pixel cells can be split as compared to a current provided to a pixel cell during reset for full frame integration mode (e.g., where one pixel cell is reset during a given time period, . . . ). Accordingly, these typical approaches can yield artifacts that degrade resultant images.